Petrology and structure of the pre-Tertiary rocks of Lummi and Eliza Islands, Washington

Abstract

Exposed on Lummi Island are two groups of pre-Tertiary rocks everywhere in fault contact with each other: a 1300 meter thick section of turbidite sandstone and mudstone, and rocks largely of igneous affinity. The latter rocks consist of pillow lavas with associated radiolarian chert dated as Middle to early Late Jurassic, and, in a relatively small, isolated exposure, an intrusive complex containing rocks dated by Pb/U methods as 160 + 3 my.